1. Field of the Invention
The present invention relates to a detent escapement for a timepiece and a mechanical timepiece using the same.
2. Description of the Related Art
In the related art, a detent escapement, is known as an escapement for maintaining a daily rate of a mechanical timepiece. These kinds of escapement mechanisms are generally classified into a spring detent escapement and a pivoted detent escapement (for example, refer to pages 39 to 47, “The Practical Watch Escapement”, Premier Print Limited, 1994 (First Edition), written by George Daniel.)
FIG. 11 is a perspective view showing an example of the spring detent escapement of the related art.
As shown in FIG. 11, the spring detent escapement 300 includes an escape wheel 301, a balance 303 that is freely oscillated about a balance staff 302 being a rotation axis, and a detent lever 304. The balance 303 includes an impulse jewel 305 that can contact a wheel tooth 301a of the escape wheel 301, and an unlocking stone 306 that can contact a one-side actuating spring 309 (passing spring) which is attached to the detent lever 304.
The detent lever 304 is fixed via a balance spring 307 which is installed at a base end thereof. The balance spring 307 supports the detent lever 304 so that the detent lever 304 approaches to and separates from the escape wheel 301, and biases the detent lever 304 to be returned to the original position. That is, the detent lever 304 is constituted being capable of approaching to and separating from the escape wheel 301 with the base end of the balance spring 307 as a fulcrum 304a. 
In addition, a locking stone 308, which can contact the wheel tooth 301a of the escape wheel 301, is installed to the detent lever 304. In addition, the base end of the one-side actuating spring 309 is fixed to the base end side of the detent lever 304. The one-side actuating spring 309 is formed along the longitudinal direction of the detent lever 304 so that the tip of the one-side actuating spring 309 is slightly more protruded than that of the detent lever 304. That is, the one-side actuating spring 309 is formed so as to be along a straight line which passes through the balance staff 302 of the balance 303 and the fulcrum 304a of the detent lever 304. In addition, the tip of the one-side actuating spring 309 comes into contact with the unlocking stone 306 of the balance 303.
According to the above-described configuration, if the unlocking stone 306 is rotated toward the direction of an arrow CCW30 (a counterclockwise direction in FIG. 11) due to the fact that the balance 303 is freely oscillated, the detent lever 304 is pressed through the one-side actuating spring 309. Thereby, the locking stone 308, which comes into contact with the wheel tooth 301a of the escape wheel 301, is separated from the wheel tooth 301a, and the engagement between the escape wheel 301 and the detent lever 304 is released. Therefore, the escape wheel 301 is rotated by one tooth.
While the escape wheel 301 is rotated by one tooth, a bias force of the balance spring 307 acts on the detent lever 304, and the detent lever 304 is returned to the original position. Thereby, the locking stone 308 comes into contact with the wheel tooth 301a of the escape wheel 301 again. That is, the escape wheel 301 is engaged with the detent lever 304, and the rotation of the escape wheel 301 is stopped.
On the other hand, if the unlocking stone 306 reverses due to the free oscillation of the balance 303 and is rotated toward a direction of an arrow CW30 (a clockwise direction in FIG. 11), by the unlocking stone 306, the one-side actuating spring 309 is pressed toward the direction in which the one-side actuating spring 309 is separated from the detent lever 304. At this time, the detent lever 304 comes to be in the stopped state while the one-side actuating spring 309 is elastically deformed. After the unlocking stone 306 is separated from the one-side actuating spring 309, the one-side actuating spring 309 which is pressed to the unlocking stone 306 is returned to the original position by a restoration force of the one-side actuating spring 309 itself.
That is, when the unlocking stone 306 is rotated toward the direction of the arrow CCW30 and the detent lever 304 is pressed via the one-side actuating spring 309, the one-side actuating spring 309 does not perform any operation. On the other hand, if the unlocking stone 306 is rotated toward the direction of the arrow CW30, the one-side actuating spring 309 is elastically deformed and operated.
In addition, due the fact that the operation is repeatedly performed, a train wheel of the mechanical timepiece is driven at a constant speed.
FIG. 12 is a perspective view showing an example of the pivoted detent escapement of the related art. In addition, the same aspects as the spring detent escapement 300 of FIG. 11 are described with denoting the same reference numbers.
As shown in FIG. 12, the pivoted detent escapement 400 includes the escape wheel 301, a balance 403 which is freely oscillated about the balance staff 302, and a detent lever 404. Here, the difference between the pivoted detent escapement 400 and the spring detent escapement 300 is that the basing means for returning the detent lever to the original position are different to each other.
That is, the detent lever 404 of the pivoted detent escapement 400 is rotatably supported via the rotation axis 410, and therefore, the detent lever 404 can approach to and separate from the escape wheel 301. In addition, a balance spring 407 installed to the detent lever 404 is constituted by a coil spring so as to enclose a rotation axis 410, and biases the detent lever 404 to be returned to the original position.
In addition, in the detent lever 404, the base end of the one-side actuating spring 409 is fixed to a straight line P100 which is approximately perpendicular to the longitudinal direction of the detent lever 404 and passes through the rotation axis 410. The one-side actuating spring 409 is formed so as to be along the longitudinal direction of the detent lever 404, that is, the straight line which passes through the balance staff 302 of the balance 403 and the rotation axis 410 of the detent lever 404. The tip of the one-side actuating spring comes into contact with the unlocking stone 306 of the balance 403.
According to the configuration, due to the fact that the balance 403 is freely oscillated, if the unlocking stone 306 is rotated in the direction of an arrow CCW31 (a counterclockwise direction in FIG. 12) or in the direction of an arrow CW31 (a clockwise direction in FIG. 12), the one-side actuating spring 409 is operated or not operated at all according to the rotation. Thereby, the train wheel of the mechanical timepiece is driven at a constant speed.
However, in the above-described related art, when the one-side actuating springs 309 and 409 are operated, the unlocking stone 306 is rotated against the spring force. Therefore, energy loss with respect to the free oscillation of the balances 303 and 403 occurs.
Here, in the spring detent escapement 300, the base end of the one-side actuating spring 309 is fixed more to the tip side than the fulcrum 304a of the detent lever 304, that is, the balance 303 side. In addition, in the pivoted detent escapement 400, the base end of the one-side actuating spring 409 is fixed more to the slightly tip side than the rotation axis 410 of the detent lever 404, that is, to the balance 403 side.
In the configurations as described above, a portion of each one-side actuating spring 309 and 409 subjected to a maximum stress is present more at the tip sides than the fulcrum 304a of the detent lever 304 and the rotation axis 410 of the detent lever 404. Thereby, each one-side actuating spring 309 and 409 is difficult to bend, and the balances 303 and 403 are easily subjected to the influence of the spring force of the one-side actuating springs 309 and 409. Therefore, there are problems in that decreasing energy loss with respect to the free oscillation of the balances 303 and 403 is difficult and the timekeeping accuracy is deteriorated.
In addition, since each one-side actuating spring 309 and 409 is formed along the longitudinal direction of the respective detent levers 304 and 404, when the unlocking stone 306 is reversed (refer to arrows CW30 and CW31 in FIGS. 11 and 12) and the one-side actuating springs 309 and 409 are operated, the contact ranges between the unlocking stone 306 and the tips of the one-side actuating springs 309 and 409 become large. Thereby, there is a problem in that decreasing energy loss with respect to the free oscillation of balances 303 and 403 is more difficult.
The details will be described with reference to FIG. 13.
FIG. 13 is a behavior explanatory diagram of the one-side actuating spring. In addition, since the behaviors of one-side actuating springs 309 and 409 are approximately the same as each other, only the one-side actuating spring 309 which is attached to the detent lever 304 of the spring detent escapement 300 will be described.
As shown in FIG. 13, the one-side actuating spring 309 is formed along a straight line L100 which passes through the balance staff 302 of the balance 303 and the fulcrum 304a of the detent lever 304. Here, when the balance 303 is reversed (refer to an arrow CW32 in FIG. 13), the contact range between the unlocking stone 306 and the one-side actuating spring 309 becomes an angle θA in a rotational trajectory R1 of the unlocking stone 306.
On the other hand, for example, if the base end of the one-side actuating spring 309 is shifted to the right side in FIG. 13 so as to intersect with respect to the straight line L100 and the one-side actuating spring 309 is obliquely disposed (hereinafter, the one-side actuating spring is referred to as a “one-side actuating spring 309′”), the contact range between the unlocking stone 306 and the one-side actuating spring 309′ becomes an angle θB in the rotational trajectory R1 of the unlocking stone 306.
That is, in order to set the contact range between the unlocking stone 306 and the one-side actuating spring 309 to be small, it is necessary to obliquely dispose the one-side actuating spring 309′ with respect to the detent lever 304. However, with the above configuration, there is a problem in that entire detent escapement becomes large in the thickness direction.
In addition, in the spring detent escapement 300 or the pivoted detent escapement 400, since the detent levers 304 and 404 are large, the detent escapements become a so-called oversized head, and the centers of gravity are leaned forward. Thereby, the centers of gravity and the fulcrums of the one-side actuating springs 309 and 409 are deviated from each other, and loads applied to the balance springs 307 and 407 are varied due to the inclination of the detent escapement. Therefore, concern of deteriorating the timekeeping accuracy occurs.
In addition, the number of components constituting each escapement 300 and 400 is increased. Therefore, due to assembly errors, variations in the accuracy of the finished product, that is, variations of the center of gravity, the oscillation angle (amplitude), the daily rate, or the like, are increased.